The story is preserved in the Wu tai si of 1017

Hu Kiao traveled in the country of the Kitan from AD 947 to 953 and narrates that there for the first time he ate water-melons (si kwa). He goes on to say: It is told that the Kitan, after the annihilation of the Uigur, obtained this cultivation. They cultivated the plant by covering the seeds with cattle manure and placing mats over the beds. The fruit is as large as that of the tun kwa (Benincasa cerifera) and of sweet taste. 
( The Uigur were a Turkish tribe and the Kitan lived in Northern China; we see here how a plant native from the southern part of Africa slowly makes its way to China. In another document its introduction into China proper will be related.)